By mounting an ironclad defence of his form this week, John Terry succeeded only in confirming the sceptics' view that, on the field as well as off it, his aura is not what it was. The smart thing to do would have been to make a quiet admission of a temporary dip, or to say nothing. But Terry, who returns to the Chelsea squad at Anfield tomorrow after serving a one-match ban, has not always distinguished himself off the pitch through an instinct for doing the smart thing.

Although the decision to defend himself was perhaps that of a "man's man" – in his team-mate Frank Lampard's famous description, following Terry's muffed penalty in Moscow two years ago – it flies in the face of a great deal of fresh evidence, most recently the defeat at Tottenham Hotspur in which he was dismissed for two yellow-card offences after a performance riddled with errors and uncertainties, incurring a suspension that forced him to miss a Premier League fixture for the first time since January 2009.

For several weeks before the debacle at White Hart Lane he had been showing unusual signs of wear and tear. His mistakes contributed to defeats by Everton and Manchester City in February, and a bad tackle on James Milner in the FA Cup semi-final victory over Aston Villa last month added another charge to a lengthening sheet.

"I'm totally fine with my form," he announced this week, rejecting the suggestion that this is more than a short‑term problem. "If I'm going to play 50 or 60 games, I'm expected to have two or three bad games. That's standard, you're not going to play well in every game. Not even Wayne Rooney and Lionel Messi can do that."

But Rooney and Messi are forwards. At the very highest level defenders – like goalkeepers – are judged by their closeness to infallibility, and until recently the Chelsea captain's record on that score has been impressive. At the end of the last World Cup finals he was the only Englishman included in the Fifa technical committee's all-star squad of 23 players, and he has been a member of Uefa's team of the year for four of the past five seasons.

Alan Hansen is judging by those standards when he contradicts Terry's own assessment of his form. "You look at John Terry and you think of a solid, reliable, resolute leader," the former Liverpool centre-back says. "Unbelievably good positionally, great on the ball and dominant in the air, and perhaps just absent of a little pace. He's been the cornerstone of Chelsea's success for a long period of time. This year, due to injuries and whatever, he's struggled.

"He's never been the quickest but what happens is that when you get older, when you've had substantial injuries, then you need to be as quick as you've ever been. He's had a bad back, he's had niggles here and there and I think he's gone to ground more than he's ever done. Straight away that would be a warning sign to me. You're basically making decisions in the knowledge that you might not be quick enough to get there."

Terry's crisis of fallibility, as many see it, follows too closely for comfort upon problems in his private life. In January he was turned over by the News of the World, who reported his affair with the ex-girlfriend of his England and former Chelsea team-mate Wayne Bridge, adding to a pile of tabloid allegations concerning himself and his family.

In football terms, the first consequence was the loss of the England captaincy, initially awarded to him by Steve McClaren in August 2006 and retained, despite the failure to reach the finals of Euro 2008, throughout the highly successful series of qualifying matches for the 2010 World Cup. Fabio Capello wasted no time in taking a hardline decision, removing a possible source of further controversy and disruption while hanging on to Terry's availability as a player.

On the surface, Terry took it well. He accepted Capello's decision without public demur and his first home appearance following the revelations saw him give a flawless display in a defeat of Arsenal. But the near-triumphalism of his post-match praise for the Stamford Bridge fans' supportive response – "I leave this place with delight," he said – seemed somewhat misjudged. And while Chelsea played Cardiff in the fifth round of the FA Cup the following weekend, Carlo Ancelotti was forced to give his captain a few days off so that Terry could join his wife in Dubai for a well publicised rapprochement and, it is said, make arrangements to secure his former lover's silence.

In his personal life, he seems to have weathered the storm – and his resilience on the pitch has never been in doubt. In the April 2006 match at Stamford Bridge best remembered for Rooney's broken metatarsal, he played for almost the whole 90 minutes with blood seeping through his sock from a deep gash on his ankle. In 2007 League Cup final he almost died after being accidently kicked in the head by Arsenal's Abou Diaby and swallowing his tongue, subsequently missing three matches.

His acceptance of responsibility on the pitch was demonstrated when, in a 2006 league match against Reading, he responded to injuries to Petr Cech and Carlo Cudicini by taking over in goal for the final minutes to see out a 1-0 win. Even the penalty shoot-out miss in the 2008 Champions League final, which reduced him to tears, came about only because he had agreed to take the place of Didier Drogba, who had been sent off.

"It's all about how you respond," he said this week. "I think I've responded well." The wider jury has yet to reach a verdict and will be paying particular attention to his form in tomorrow's crucial fixture, in which Chelsea need to see off a wounded Liverpool ahead of Manchester United's late afternoon kick-off at Sunderland. "John Terry will play," Carlo Ancelotti said yesterday, "because we need to have his character and personality in this game."

Beyond that lies the World Cup, and Capello's urgent need, in the midst of a more general crisis among England's centre-backs, for a reappearance of the John Terry who so confidently led the team through the qualifying campaign before stumbling over his own celebrity.